1. Field of the Invention
The present invention generally relates to an electrical outlet box and, more particularly, is concerned with an improved knockout panel construction and attachment arrangement for closing a cable entry aperture defined in the box while facilitating easy detachment of the knockout panel when desired.
2. Description of the Prior Art
Various types of electrical outlet boxes, adapted to have electrical cables extended into the box for connection to terminals located therein, are well known in the art. These boxes are mounted in walls and ceilings during the construction of buildings, and afterwards during renovation thereof, to provide ready access to electrical service.
Representative of the prior art are the electrical outlet boxes disclosed in U.S. Pat. Nos. 2,788,151 (Shore), 2,898,688 (Cottar), 3,895,732 (Robinson et al), 4,202,457 (Tansi), 4,277,641 (Bauer et al), 4,304,958 (Neff et al), 4,306,109 (Nattel), 4,348,547 (Bowden), 4,436,952 (Lockwood), 4,304,957; 4,366,343; 4,389,535; 4,414,427 and 4,424,406 (Slater et al); in British patent No. 1,396,790 (Gore); in Canadian patents Nos. 577,589 (Elder) and 658,727 (Rudolph et al); and in a German patent No. DE 30 25 866 A1 (Grossauer).
All outlet boxes employ cable entry apertures generally in their rear portions which are adapted to permit access of the electrical power cables into the interior of the boxes. One or more electrical power cables are inserted into the box, each through a separate entry aperture, for connection of the conductor wires of the cable to an electrical fixture, such as a switch or receptacle, to be mounted to the front portion of the box.
In one type of molded plastic outlet box, as represented by those in the patents to Robinson et al and Slater et al, it is a common practice to substantially completely close the cable entry apertures with "knockout" panels. This is done in order to prevent debris from entering the box through any of the apertures that are not utilized, and to minimize the spread of fire from the interior of the box in the event of an electrical malfunction in the fixture or connection in the box. These panels are ordinarily removably attached to the box wall structure defining each aperture by connective material which bridges between and interconnects the panels and the wall structure.
To remove a knockout panel, the pointed end of a tool such as a screwdriver is used to rupture the connecting material, usually before the outlet box is mounted to the building wall stud. A standard practice is for the workman to hold the outlet box in one hand and strike the end of the screwdriver being gripped in the other hand against the knockout panel or pry under the panel with the end of the screwdriver.
In the case of many knockout panels, removal can be both hazardous and frustrating. In some instances, if proper care is not exercised, the end of the screwdriver is apt to glance off the panel surface and strike the workman's other hand holding the outlet box. In other instances, the panel can twist on the connective material instead of breaking cleanly, thereby taking more time than it should to complete its removal. The collective effect of these seemingly minor difficulties is to reduce worker productivity and increase construction costs. Consequently, a need still exists for improvements in the design and construction of electrical outlet boxes to overcome these shortcomings.